A standard motor-vehicle door latch has a housing mounted on a door edge and holding a fork engageable about a bolt or eye itself mounted on a door post, a retaining pawl that can hold the fork in a position engaged around the bolt and holding it in the housing with the door latched, and various operating levers that allow the pawl to be actuated from inside and outside the door. Typically the latch also has a locking mechanism that can either block movement of or disconnect the operating levers and that includes a key-operated cylinder accessible from outside the door to lock and unlock its latch.
In today's cars it is furthermore standard to provide a central lock controller so that, for instance, when the driver's door is locked or unlocked, all the other doors of the vehicle are similarly locked or unlocked via respective actuators built into them. Furthermore such a system frequently has an antitheft mode in which it is impossible to open any of the vehicle's doors, even from inside the vehicle, so that in this antitheft mode the doors cannot be opened by clandestine means.
Thus in one such system the key is turned clockwise from a central starting position through about 30.degree. to lock the latches. Turning the key the same distance counterclockwise both locks the latches and sets the antitheft mode. In another arrangement the key is turned 30.degree. counterclockwise to lock the latches and then another 30.degree. to set the antitheft mode. Another system locks the latches when the key is turned counterclockwise and then sets the antitheft position if the key is immediately returned to the center position and then turned back counterclockwise 30.degree.. Normally a blinking pilot light is provided on the dashboard to indicate that the antitheft mode is set.
Such systems normally rely on mechanical microswitches to detect the setting of the latch. Other systems such as described in commonly owned patent application Ser. Nos. 08/653,771, 08/902,469, and 08/915,897 employ hall-effect sensors, but in a somewhat different application. All such systems are fairly complex.